That was former Mexicana XA-NAS, which worked through various dealers in the US from the 1970s-90s without ever being used. A onetime regular PPRuNe poster was the flight engineer on that last flight from Albuquerque into O'Hare - apparently none of the crew had even been in a Comet before !
I was the FO on this flight and it's true none of us had flown the Comet prior to that day. We did one takeoff and full stop at KABQ before heading off to KORD. BELARG was the FE and we use to keep in touch a little but I'm afraid he had some health issues that prevented his continued participation in this forum. His postings were always excellent by the way. The fellow who flew Capt on the flight passed away last year.